The chapter focuses on the fungus-farming leaf-cutting ants of the genera Atta and Acromyrmex, which are dominant herbivores and agricultural pests in tropical and subtropical America, have been studied particularly closely. The workers spend much of their day snipping off fragments of fresh leaves, which they carry to their underground fungus gardens and chew into pulp. As the garden matures, the mycelium produces bundles of swollen hyphal tips known as gongylidia. The worker ants chew these and ingest the cytoplasm to supplement their diet of sap. Research over the past quarter century has revealed many astonishing details of this underground industry. They include insights into the elaborate manuring regimes which the ants use to optimize the yield of fungus and their incorporation of Streptomyces and other antibiotic producers to combat the proliferation of unwanted molds, weeds in the fungal garden. Moreover, Atta texana feces contained proteases identical to those in cultures of the symbiotic fungus. The major finding, however, emerged from a comparison of the specific activities of the enzymes in the fungus and in the fecal droplets that the ants deposited on their leaf fragments. The measurements indicated that the enzymes were not only protected, but quite possibly concentrated, too, as they passed through the ant's intestinal tracts.